The problem to be solved is to provide one means of sustaining an exothermic reaction in the throat of a nozzle such that a fluid medium can undergo a change in phase from an incompressible to a compressible liquid at that point. When thrusting laterally around a shaft, such a nozzle can be used to provide rotational drive. Such a nozzle is described in a prior U.S. patent application Ser. No. 10/797,255 of the present inventor, entitled “Implementation and Application of Phase Change in a Fluid Flowing Through A Nozzle”.